It’s illegal for people under 20 to smoke, so it will depends if the police gets involved or not. If they do, the parents and the teacher in charge may be heavily fined and even go to jail. If possible, the school will keep things quiet though.
The minimum would be to exclude him for one or two weeks, assuming he would not do it again. That being said, he has implemented an elaborate plan to not be found out, which is an aggravating factor, so it could be a month or more (again, depending on the school). In any case, the teacher in charge of the club is probably in troubles if it’s found out.